High molecular weight olefin-based resins, particularly resins with high molecular weight fractions of >106 g/mole in amounts greater than two weight percent, are desirable to produce articles with improved mechanical properties, such as those produced from HDPE blow molding resin, where resin swell is important. One of the most efficient processes for the production of ethylene polymers and copolymers is the gas phase fluidized bed process. In order to maximize efficiency and minimize operation costs of the system, it is best to run such process in what is known as “condensed” or “super-condensed” mode in which a large fraction of the recycle gas is condensed and recycled back into the reactor.
The capability to control molecular weight distribution (“MWD”) of an olefin polymerization system is also desirable. Various techniques for modifying molecular weight distribution are known in the art. Manipulation of polymerization process variables, for example, allows for some change in molecular weight distribution. However economics (i.e., too low a reaction temperature results in poor throughput), physical factors (reaction temperature, for example, can be limiting if the polymer becomes soft or sticky) and process limitations (e.g., total pressure, monomer solubility in the polymer) limit the extent to which process variables may be manipulated. The ability to control polymer properties, such as MWD, using a component such as a co-fed catalyst or a co-catalyst would be highly desirable.
Many factors affect the operability of gas phase fluidized bed reactors. Preferably the catalyst is inactive at very high temperatures (i.e., close to the melting point of the polymer). Catalyst deactivation is also a consideration in reactor locations with excessive heat, e.g. those portions of the reactor in which resin may accumulate, leading to sheeting or chunk formation.
Therefore, it would be advantageous to have a catalyst system for which the molecular weight distribution of the produced resin could be changed without the need to change the formulation of the catalyst.